1. Field of the Invention
The present invention relates to a semiconductive device and method of making the same, and more particularly to a structure of a strained-silicon transistor and a method of making the same.
2. Description of the Prior Art
With the trend of miniaturization of semiconductor device dimensions, the scale of the gate, source and drain of a transistor is decreased in accordance with the decrease in critical dimension (CD). Due to the physical limitations of the materials used, the decrease in scale of the gate, source and drain results in the decrease of carriers that determine the magnitude of the current in the transistor element, and this can therefore adversely affect the performance of the transistor. Increasing carrier mobility in order to boost up a metal oxide semiconductor (MOS) transistor is therefore an important topic in the field of current semiconductor techniques.
In various current techniques, mechanical stress is generated on purpose in the channel to increase carrier mobility. For example, a compressive or tensile strained channel can be formed by forming stressors on the transistor to improve the carrier mobility. Generally, a tensile stress film is formed on the N type metal oxide semiconductor (NMOS) transistor, and a compressive stress film is formed on the P type metal oxide semiconductor (PMOS) transistor. However, the compressive stress film may separate from the surface of the PMOS, resulting in delamination because of the high compressive stress. Defects will therefore be formed on the PMOS.